1. Field of the Invention
The invention is related to the field of communications and, in particular, to delivery of SMS messages.
2. Statement of the Problem
In many mobile networks, text messaging has become a very popular mode of communication. Short Message Service (SMS) is a communication protocol allowing the interchange of short text messages (i.e., 160 characters) between mobile devices. Often times, mobile users more frequently use SMS messaging for communication than voice calls.
SMS messages are presently transmitted over signaling channels of a voice network, such as over SS7 channels. A typical voice network includes a Radio Access Network (RAN) that provides an air interface to a mobile device, and a core network that connects the RAN to other networks, such as the PSTN or another RAN. The core network includes a switching system and a subscriber server for serving the mobile device. For instance, in a UMTS network, the switching system may comprise a Mobile Switching Center (MSC) and the subscriber server may comprise a Home Location Register (HLR). In an IP Multimedia Subsystem (IMS) network, the switching system may comprise a Call Session Control Function (CSCF) and the subscriber server may comprise a Home Subscriber Server (HSS). The core network also connects to a SMS Center (SMS-C). The SMS-C is the entity which does the job of storing and forwarding SMS messages to and from mobile devices.
The following illustrates an example of a delivery of a Mobile Terminated (MT) SMS message to a mobile device in a UMTS network. The SMS-C receives an SMS message destined for the mobile device, and stores the SMS message. The SMS-C then queries the subscriber server (i.e., HLR or HSS) for routing information based on the present position of the mobile device. The SMS-C then attempts to deliver the SMS message to the destination by routing the SMS message to the correct MSC through an SS7 channel. The MSC receives the SMS message from the SMS-C, and forwards the SMS message through the RAN to the mobile device using a signaling channel.
In an example of a delivery of a Mobile Originated (MO) SMS message, a sending party enters text into a mobile device, and also enters a phone number or address for the intended destination of the SMS message. When entry of the SMS message is completed, the mobile device sends the SMS message to the MSC over the RAN again using a signaling channel. The MSC that is serving the mobile device receives the SMS message, and routes the SMS message to the SMS-C. The SMS-C stores the SMS message, and attempts to forward the SMS message to the destination.
A high volume of SMS traffic on a traditional voice network can cause problems. For example, each time an SMS message is received at the SMS-C, the SMS-C needs to query the subscriber server (i.e., HLR or HSS) to determine the routing information for the destination of the SMS message. When there is a high volume of SMS messages, a significant amount of messages are exchanged between the SMS-C and the subscriber server, which can reduce the overall operating speed of the voice network. Also, the signaling channels of the voice network can become congested with SMS traffic, as SMS messages are transported over the signaling channels. Even further, the switching systems, such as an MSC or CSCF, have to handle each SMS message, which can cause congestion at the switching systems. A service provider may implement more switching systems to handle higher SMS loads, but the expense of implementing the additional switching systems is undesirable.